A composite video signal is the sum of a luminance (brightness) signal and a chrominance (color) signal. These signals may be referred to as luma and chroma signals, respectively. The frequency ranges of the luma and chroma signals are designed to overlap. In video processing, the luma and chroma signal components are added together in order to generate a composite video signal. The luma and chroma video elements are integrated and broadcasted as a single composite video stream. Once the broadcasted composite signal is received, the luma and chroma signal components must be separated in order for the video signal to be processed and displayed. A comb filter may be utilized for separating the chroma and luma video signal components. For example, a television may be adapted to receive a composite video input and utilize an integrated comb filter to separate the chroma and luma video signal components. However, before the television can display the received video signal, the chroma and luma video components have to be separated.
Several combing techniques exist, including spatial or 2D techniques and temporal or 3D techniques. In conventional video processing, there are three ways to separate the luma and chroma video components and these include combing horizontally, combing vertically, and combing temporally. During separation of the luma and chroma components, there are three bandwidth directions that may incur losses in the separation process and in the separated signal. Depending on the combing method that is utilized, the separated signal may have reduced vertical bandwidth, horizontal bandwidth, and/or temporal bandwidth
The first way to separate the luma and chroma video components is by horizontal combing. Horizontal combing may be accomplished by utilizing a notch filter, for example. Since the chroma signal component in a composite video signal may be modulated at 3.58 MHz, a notch filter set at 3.58 MHz may be utilized. Combing vertically may also be utilized to separate the luma and chroma video components. Combing vertically may be achieved in three different ways—the current line may be combed with the previous and the next line, the current line may be combed with the line just before it, or the current line may be combed with the line just after it. The vertical combing is performed spatially, which involves combing only within one field at a time and without any temporal combing.
During combing in a current frame, for example, if the current line is added to the previous line, the chroma content may cancel out and two times the luma content may be obtained. On the other hand, if the previous line is subtracted from the current line, the luma content may cancel out and two times the chroma content may be obtained. In this way, luma and chroma content may be separated from the composite video signal for further processing. However, vertical combing may result in a reduced vertical bandwidth.
Another way to comb a composite signal is to comb temporally. Combing temporally comprises combing between two adjacent frames, for example, the current frame and the previous frame. Further, temporal combing may be characterized by a reduced temporal bandwidth. Luma and chroma content may be separated by utilizing the same addition and subtraction method between a current line and a previous line as it was utilized with vertical combing.
The problem with using one combing technique over another is that while one technique may work well in certain portions of a video sequence or a video image, it may not work as well with other portions. As a result, using “the best” combing technique may result in high error rates.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.